The first parameter of an extension method is prefixed by the this keyword, followed by the type it is extending (Person in this example, indicating to the compiler that this extension method must be added to the Person class). The rest of the parameter list (if any) is then the signature of the extension method.

(In the figure you can see the new extension method for the Person object )If an extension method has the same signature as another method in the class it is trying to extend, the method in the class will take precedence and the extension method will be ignored.